Systems and methods for induction charging with a closed magnetic loop

ABSTRACT

Systems, methods, and computer program products for induction charging with a closed magnetic loop are described herein. In one aspect, an apparatus for wireless power transmission comprises a plurality of coplanar coils, each of the plurality of coplanar coils configured to be individually energized and produce a magnetic field. Further, the controller is configured to reverse polarity of the magnetic field of at least one of the plurality of coplanar coils based on a measure of coupling between coils and to select at least two of the plurality of coplanar coils for wireless power transmission based on the measure of coupling between coils.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority benefit under 35 U.S.C. §119(e) to U.S.Provisional Patent Application No. 61/560,135 entitled “SYSTEMS ANDMETHODS FOR INDUCTION CHARGING WITH A CLOSED MAGNETIC LOOP” filed onNov. 15, 2011, the disclosure of which is hereby incorporated byreference in its entirety.

FIELD

The present invention relates generally to wireless power. Morespecifically, the disclosure is directed to induction charging with aclosed magnetic loop.

BACKGROUND

An increasing number and variety of electronic devices are powered viarechargeable batteries. Such devices include mobile phones, portablemusic players, laptop computers, tablet computers, computer peripheraldevices, communication devices (e.g., Bluetooth devices), digitalcameras, hearing aids, and the like. While battery technology hasimproved, battery-powered electronic devices increasingly require andconsume greater amounts of power. As such, these devices constantlyrequire recharging. Rechargeable devices are often charged via wiredconnections through cables or other similar connectors that arephysically connected to a power supply. Cables and similar connectorsmay sometimes be inconvenient or cumbersome and have other drawbacks.Wireless charging systems that are capable of transferring power in freespace to be used to charge rechargeable electronic devices or providepower to electronic devices may overcome some of the deficiencies ofwired charging solutions. As such, wireless power transfer systems andmethods that efficiently and safely transfer power to electronic devicesare desirable.

SUMMARY OF THE INVENTION

Various implementations of systems, methods and devices within the scopeof the appended claims each have several aspects, no single one of whichis solely responsible for the desirable attributes described herein.Without limiting the scope of the appended claims, some prominentfeatures are described herein.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Note thatthe relative dimensions of the following figures may not be drawn toscale.

One aspect of the disclosure provides an apparatus for wireless powertransmission comprising a plurality of coplanar coils, each of theplurality of coplanar coils is configured to be individually energizedand produce a magnetic field; and a controller is configured to reversepolarity of the magnetic field of at least one of the plurality ofcoplanar coils based on a measure of coupling between coils and toselect at least two of the plurality of coplanar coils for wirelesspower transmission based on the measure of coupling between coils.

Another aspect of this disclosure provides a method for wireless powertransmission comprising energizing a plurality of coplanar coils so thateach of the plurality of coplanar coils produces a magnetic field;reversing polarity of the magnetic field of at least one of theplurality of coplanar coils based on a measure of coupling betweencoils; and, selecting at least two of the plurality of coplanar coilsfor wireless power transmission based on the measure of coupling betweencoils.

One aspect of this disclosure provides an apparatus for wireless powertransmission comprising means for energizing a plurality of coplanarcoils so that each of the plurality of coplanar coils produces amagnetic field; means for reversing polarity of the magnetic field of atleast one of the plurality of coplanar coils based on a measure ofcoupling between coils; and, means for selecting at least two of theplurality of coplanar coils for wireless power transmission based on themeasure of coupling between coils.

Another aspect of this disclosure provides a non-transitory computerstorage that stores executable program instructions that direct anapparatus for wireless power transmission to perform a process thatcomprises: energizing a plurality of coplanar coils so that each of theplurality of coplanar coils produces a magnetic field; reversingpolarity of the magnetic field of at least one of the plurality ofcoplanar coils based on a measure of coupling between coils; and,selecting at least two of the plurality of coplanar coils for wirelesspower transmission based on the measure of coupling between coils.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of an example wireless powertransfer system.

FIG. 2 is a functional block diagram of example components that may beused in the wireless power transfer system of FIG. 1.

FIG. 3 is a schematic diagram of a portion of transmit circuitry orreceive circuitry of FIG. 2 including a transmit or receive coil.

FIG. 4 is a functional block diagram of a transmitter that may be usedin the wireless power transfer system of FIG. 1.

FIG. 5 is a functional block diagram of a receiver that may be used inthe wireless power transfer system of FIG. 1.

FIG. 6 is a schematic diagram of a portion of transmit circuitry thatmay be used in the transmit circuitry of FIG. 4.

FIG. 7 is an example wireless communication system in which aspects ofthe present disclosure may be employed.

FIG. 8 illustrates a side view of an example coil-to-coil couplingsystem.

FIG. 9 illustrates a side view of another example coil-to-coil couplingsystem.

FIG. 10 illustrates a side view of an example dual coil coupling system.

FIG. 11 is a schematic of an example wirelessly chargeable device.

FIG. 12 is a schematic of an example charging pad.

FIG. 13 is a schematic of an example charging system.

FIG. 14 is a functional block diagram of example components that may beused in a wireless power system.

FIG. 15 is a schematic of an example multi-coil charging pad that may beused in a wireless power system.

FIG. 16 is a schematic of an example multi-coil charging pad and devicein a wireless power system.

FIG. 17 is a schematic of another example multi-coil charging pad anddevice in a wireless power system.

FIG. 18 is a schematic of yet another example multi-coil charging padand device in a wireless power system.

FIG. 19 is a schematic diagram of an example switching circuit to changethe polarity of charging pad coils.

FIG. 20 is a schematic of an example multi-coil charging pad and devicein a wireless power system.

FIG. 21 is a schematic diagram of an example switching circuit to changethe polarity of charging pad coils.

FIG. 22 is a schematic of an example multi-coil charging pad andmultiple devices in a wireless power system.

FIG. 23 is an example wireless power transmitter which includes a powertransfer sensing mechanism.

FIG. 24 is a flowchart of an example alignment discovery logic for acharging pad.

FIG. 25 is a schematic of an example wirelessly chargeable device.

FIG. 26 is a schematic of an example multi-coil charging pad and devicein a wireless power system.

FIG. 27 is a schematic of another example multi-coil charging pad anddevice in a wireless power system.

FIG. 28 is flowchart of an example method of transmitting wirelesspower.

FIG. 29 is a functional block diagram of a wireless power apparatus.

The various features illustrated in the drawings may not be drawn toscale. Accordingly, the dimensions of the various features may bearbitrarily expanded or reduced for clarity. In addition, some of thedrawings may not depict all of the components of a given system, methodor device. Finally, like reference numerals may be used to denote likefeatures throughout the specification and figures.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments of theinvention and is not intended to represent the only embodiments in whichthe invention may be practiced. The term “exemplary” used throughoutthis description means “serving as an example, instance, orillustration,” and should not necessarily be construed as preferred oradvantageous over other exemplary embodiments. The detailed descriptionincludes specific details for the purpose of providing a thoroughunderstanding of the exemplary embodiments of the invention. Theexemplary embodiments of the invention may be practiced without thesespecific details. In some instances, well-known structures and devicesare shown in block diagram form in order to avoid obscuring the noveltyof the exemplary embodiments presented herein.

Wirelessly transferring power may refer to transferring any form ofenergy associated with electric fields, magnetic fields, electromagneticfields, or otherwise from a transmitter to a receiver without the use ofphysical electrical conductors (e.g., power may be transferred throughfree space). The power output into a wireless field (e.g., a magneticfield) may be received, captured by, or coupled by a “receiving coil” toachieve power transfer.

FIG. 1 is a functional block diagram of an exemplary wireless powertransfer system 100, in accordance with exemplary embodiments of theinvention. Input power 102 may be provided to a transmitter 104 from apower source (not shown) for generating a field 105 for providing energytransfer. A receiver 108 may couple to the field 105 and generate outputpower 110 for storing or consumption by a device (not shown) coupled tothe output power 110. Both the transmitter 104 and the receiver 108 areseparated by a distance 112. In one exemplary embodiment, transmitter104 and receiver 108 are configured according to a mutual resonantrelationship. When the resonant frequency of receiver 108 and theresonant frequency of transmitter 104 are substantially the same or veryclose, transmission losses between the transmitter 104 and the receiver108 are minimal. As such, wireless power transfer may be provided overlarger distance in contrast to purely inductive solutions that mayrequire large coils that require coils to be very close (e.g., mms).Resonant inductive coupling techniques may thus allow for improvedefficiency and power transfer over various distances and with a varietyof inductive coil configurations.

The receiver 108 may receive power when the receiver 108 is located inan energy field 105 produced by the transmitter 104. The field 105corresponds to a region where energy output by the transmitter 104 maybe captured by a receiver 105. In some cases, the field 105 maycorrespond to the “near-field” of the transmitter 104 as will be furtherdescribed below. The transmitter 104 may include a transmit coil 114 foroutputting an energy transmission. The receiver 108 further includes areceive coil 118 for receiving or capturing energy from the energytransmission. The near-field may correspond to a region in which thereare strong reactive fields resulting from the currents and charges inthe transmit coil 114 that minimally radiate power away from thetransmit coil 114. In some cases the near-field may correspond to aregion that is within about one wavelength (or a fraction thereof) ofthe transmit coil 114. The transmit and receive coils 114 and 118 aresized according to applications and devices to be associated therewith.As described above, efficient energy transfer may occur by coupling alarge portion of the energy in a field 105 of the transmit coil 114 to areceive coil 118 rather than propagating most of the energy in anelectromagnetic wave to the far field. When positioned within the field105, a “coupling mode” may be developed between the transmit coil 114and the receive coil 118. The area around the transmit and receive coils114 and 118 where this coupling may occur is referred to herein as acoupling-mode region.

FIG. 2 is a functional block diagram 200 of exemplary components thatmay be used in the wireless power transfer system 100 of FIG. 1, inaccordance with various exemplary embodiments of the invention. Thetransmitter 204 may include transmit circuitry 206 that may include anoscillator 222, a driver circuit 224, and a filter and matching circuit226. The oscillator 222 may be configured to generate a signal at adesired frequency, such as 468.75 KHz, 6.78 MHz or 13.56 MHz, that maybe adjusted in response to a frequency control signal 223. Theoscillator signal may be provided to a driver circuit 224 configured todrive the transmit coil 214 at, for example, a resonant frequency of thetransmit coil 214. The driver circuit 224 may be a switching amplifierconfigured to receive a square wave from the oscillator 222 and output asine wave. For example, the driver circuit 224 may be a class Eamplifier. The driver circuit 224 may also be provided with a drivesignal 225 having a voltage V_(D) that is configured to control themaximum power that may be delivered through the transmit circuitry 206.A filter and matching circuit 226 may be also included to filter outharmonics or other unwanted frequencies and match the impedance of thetransmitter 204 to the transmit coil 214.

The receiver 208 may include receive circuitry 210 that may include amatching circuit 232 and a rectifier and switching circuit 234 togenerate a DC power output from an AC power input to charge a battery236 as shown in FIG. 2 or to power a device (not shown) coupled to thereceiver 108. The matching circuit 232 may be included to match theimpedance of the receive circuitry 210 to the receive coil 218. Thereceiver 208 and transmitter 204 may additionally communicate on aseparate communication channel 219 (e.g., Bluetooth, zigbee, cellular,etc). The receiver 208 and transmitter 204 may alternatively communicatevia in-band signaling using characteristics of the wireless field 205.

As described more fully below, receiver 208, that may initially have aselectively disablable associated load (e.g., battery 236), may beconfigured to determine whether an amount of power transmitted bytransmitter 204 and receiver by receiver 208 is appropriate for charginga battery 236. Further, receiver 208 may be configured to enable a load(e.g., battery 236) upon determining that the amount of power isappropriate. In some embodiments, a receiver 208 may be configured todirectly utilize power received from a wireless power transfer fieldwithout charging of a battery 236. For example, a communication device,such as a near-field communication (NFC) or radio-frequencyidentification device (RFID) may be configured to receive power from awireless power transfer field and communicate by interacting with thewireless power transfer field and/or utilize the received power tocommunicate with a transmitter 204 or other devices.

FIG. 3 is a schematic diagram of a portion of transmit circuitry 206 orreceive circuitry 210 of FIG. 2 including a transmit or receive coil352, in accordance with exemplary embodiments of the invention. Asillustrated in FIG. 3, transmit or receive circuitry 350 used inexemplary embodiments may include a coil 352. The coil may also bereferred to or be configured as a “loop” antenna 352. The coil 352 mayalso be referred to herein or be configured as a “magnetic” antenna oran induction coil. The term “coil” is intended to refer to a componentthat may wirelessly output or receive energy for coupling to another“coil.” The coil may also be referred to as an “antenna” of a type thatis configured to wirelessly output or receive power. The coil 352 may beconfigured to include an air core or a physical core such as a ferritecore (not shown). Air core loop coils may be more tolerable toextraneous physical devices placed in the vicinity of the core.Furthermore, an air core loop coil 352 allows the placement of othercomponents within the core area. In addition, an air core loop may morereadily enable placement of the receive coil 218 (FIG. 2) within a planeof the transmit coil 214 (FIG. 2) where the coupled-mode region of thetransmit coil 214 (FIG. 2) may be more powerful.

As stated, efficient transfer of energy between the transmitter 104 andreceiver 108 may occur during matched or nearly matched resonancebetween the transmitter 104 and the receiver 108. However, even whenresonance between the transmitter 104 and receiver 108 are not matched,energy may be transferred, although the efficiency may be affected.Transfer of energy occurs by coupling energy from the field 105 of thetransmitting coil to the receiving coil residing in the neighborhoodwhere this field 105 is established rather than propagating the energyfrom the transmitting coil into free space.

The resonant frequency of the loop or magnetic coils is based on theinductance and capacitance. Inductance may be simply the inductancecreated by the coil 352, whereas, capacitance may be added to the coil'sinductance to create a resonant structure at a desired resonantfrequency. As an example, capacitor 356 and capacitor 354 may be addedto the transmit or receive circuitry 350 to create a resonant circuitthat selects a signal 358 at a resonant frequency. Accordingly, forlarger diameter coils, the size of capacitance needed to sustainresonance may decrease as the diameter or inductance of the loopincreases. Furthermore, as the diameter of the coil increases, theefficient energy transfer area of the near-field may increase. Otherresonant circuits formed using other components are also possible. Asanother example, a capacitor may be placed in parallel between the twoterminals of the coil 352. For transmit coils, a signal 358 with afrequency that substantially corresponds to the resonant frequency ofthe coil 352 may be an input to the coil 352.

In one embodiment, the transmitter 104 may be configured to output atime varying magnetic field with a frequency corresponding to theresonant frequency of the transmit coil 114. When the receiver is withinthe field 105, the time varying magnetic field may induce a current inthe receive coil 118. As described above, if the receive coil 118 isconfigured to be resonant at the frequency of the transmit coil 118,energy may be efficiently transferred. The AC signal induced in thereceive coil 118 may be rectified as described above to produce a DCsignal that may be provided to charge or to power a load.

FIG. 4 is a functional block diagram of a transmitter 404 that may beused in the wireless power transfer system of FIG. 1, in accordance withexemplary embodiments of the invention. The transmitter 404 may includetransmit circuitry 406 and a transmit coil 414. The transmit coil 414may be the coil 352 as shown in FIG. 3. Transmit circuitry 406 mayprovide RF power to the transmit coil 414 by providing an oscillatingsignal resulting in generation of energy (e.g., magnetic flux) about thetransmit coil 414. Transmitter 404 may operate at any suitablefrequency. By way of example, transmitter 404 may operate at the 13.56MHz ISM band.

Transmit circuitry 406 may include a fixed impedance matching circuit409 for matching the impedance of the transmit circuitry 406 (e.g., 50ohms) to the transmit coil 414 and a low pass filter (LPF) 408configured to reduce harmonic emissions to levels to preventself-jamming of devices coupled to receivers 108 (FIG. 1). Otherexemplary embodiments may include different filter topologies, includingbut not limited to, notch filters that attenuate specific frequencieswhile passing others and may include an adaptive impedance match, thatmay be varied based on measurable transmit metrics, such as output powerto the coil 414 or DC current drawn by the driver circuit 424. Transmitcircuitry 406 further includes a driver circuit 424 configured to drivean RF signal as determined by an oscillator 423. The transmit circuitry406 may be comprised of discrete devices or circuits, or alternately,may be comprised of an integrated assembly. An exemplary RF power outputfrom transmit coil 414 may be on the order of 2.5 Watts.

Transmit circuitry 406 may further include a controller 415 forselectively enabling the oscillator 423 during transmit phases (or dutycycles) for specific receivers, for adjusting the frequency or phase ofthe oscillator 423, and for adjusting the output power level forimplementing a communication protocol for interacting with neighboringdevices through their attached receivers. It is noted that thecontroller 415 may also be referred to herein as processor 415. Thecontroller 415 may be coupled to a memory circuit 470. Adjustment ofoscillator phase and related circuitry in the transmission path mayallow for reduction of out of band emissions, especially whentransitioning from one frequency to another.

The transmit circuitry 406 may further include a load sensing circuit416 for detecting the presence or absence of active receivers in thevicinity of the near-field generated by transmit coil 414. By way ofexample, a load sensing circuit 416 monitors the current flowing to thedriver circuit 424, that may be affected by the presence or absence ofactive receivers in the vicinity of the field generated by transmit coil414 as will be further described below. Detection of changes to theloading on the driver circuit 424 are monitored by controller 415 foruse in determining whether to enable the oscillator 423 for transmittingenergy and to communicate with an active receiver. The load sensingcircuit 416 provides an output signal 435 to the controller 415. Asdescribed more fully below, a current measured at the driver circuit 424may be used to determine whether an invalid device is positioned withina wireless power transfer region of the transmitter 404.

The transmit coil 414 may be implemented with a Litz wire or as anantenna strip with the thickness, width and metal type selected to keepresistive losses low. In a one implementation, the transmit coil 414 maygenerally be configured for association with a larger structure such asa table, mat, lamp or other less portable configuration. Accordingly,the transmit coil 414 generally may not need “turns” in order to be of apractical dimension. An exemplary implementation of a transmit coil 414may be “electrically small” (i.e., fraction of the wavelength) and tunedto resonate at lower usable frequencies by using capacitors to definethe resonant frequency.

The transmitter 404 may gather and track information about thewhereabouts and status of receiver devices that may be associated withthe transmitter 404. Thus, the transmit circuitry 406 may include apresence detector 480, an enclosed detector 460, or a combinationthereof, connected to the controller 415 (also referred to as aprocessor herein). The controller 415 may adjust an amount of powerdelivered by the driver circuit 424 in response to presence signals fromthe presence detector 480 and the enclosed detector 460. The transmitter404 may receive power through a number of power sources, such as, forexample, an AC-DC converter (not shown) to convert conventional AC powerpresent in a building, a DC-DC converter (not shown) to convert aconventional DC power source to a voltage suitable for the transmitter404, or directly from a conventional DC power source (not shown).

As a example, the presence detector 480 may be a motion detectorutilized to sense the initial presence of a device to be charged that isinserted into the coverage area of the transmitter 404. After detection,the transmitter 404 may be turned on and the RF power received by thedevice may be used to toggle a switch on the Rx device in apre-determined manner, which in turn results in changes to the drivingpoint impedance of the transmitter 404.

As another example, the presence detector 480 may be a detector capableof detecting a human, for example, by infrared detection, motiondetection, or other suitable means. In some exemplary embodiments, theremay be regulations limiting the amount of power that a transmit coil 414may transmit at a specific frequency. In some cases, these regulationsare meant to protect humans from electromagnetic radiation. However,there may be environments where a transmit coil 414 is placed in areasnot occupied by humans, or occupied infrequently by humans, such as, forexample, garages, factory floors, shops, and the like. If theseenvironments are free from humans, it may be permissible to increase thepower output of the transmit coil 414 above the normal powerrestrictions regulations. In other words, the controller 415 may adjustthe power output of the transmit coil 414 to a regulatory level or lowerin response to human presence and adjust the power output of thetransmit coil 414 to a level above the regulatory level when a human isoutside a regulatory distance from the electromagnetic field of thetransmit coil 414.

As a example, the enclosed detector 460 (may also be referred to hereinas an enclosed compartment detector or an enclosed space detector) maybe a device such as a sense switch for determining when an enclosure isin a closed or open state. When a transmitter is in an enclosure that isin an enclosed state, a power level of the transmitter may be increased.

In exemplary embodiments, a method by which the transmitter 404 does notremain on indefinitely may be used. In this case, the transmitter 404may be programmed to shut off after a user-determined amount of time.This feature prevents the transmitter 404, notably the driver circuit424, from running long after the wireless devices in its perimeter arefully charged. This event may be due to the failure of the circuit todetect the signal sent from either the repeater or the receive coil thata device is fully charged. To prevent the transmitter 404 fromautomatically shutting down if another device is placed in itsperimeter, the transmitter 404 automatic shut off feature may beactivated only after a set period of lack of motion detected in itsperimeter. The user may be able to determine the inactivity timeinterval, and change it as desired. As a example, the time interval maybe longer than that needed to fully charge a specific type of wirelessdevice under the assumption of the device being initially fullydischarged.

FIG. 5 is a functional block diagram of a receiver 508 that may be usedin the wireless power transfer system of FIG. 1, in accordance withexemplary embodiments of the invention. The receiver 508 includesreceive circuitry 510 that may include a receive coil 518. Receiver 508further couples to device 550 for providing received power thereto. Itshould be noted that receiver 508 is illustrated as being external todevice 550 but may be integrated into device 550. Energy may bepropagated wirelessly to receive coil 518 and then coupled through therest of the receive circuitry 510 to device 550. By way of example, thecharging device may include devices such as mobile phones, portablemusic players, laptop computers, tablet computers, computer peripheraldevices, communication devices (e.g., Bluetooth devices), digitalcameras, hearing aids (an other medical devices), and the like.

Receive coil 518 may be tuned to resonate at the same frequency, orwithin a specified range of frequencies, as transmit coil 414 (FIG. 4).Receive coil 518 may be similarly dimensioned with transmit coil 414 ormay be differently sized based upon the dimensions of the associateddevice 550. By way of example, device 550 may be a portable electronicdevice having diametric or length dimension smaller that the diameter oflength of transmit coil 414. In such an example, receive coil 518 may beimplemented as a multi-turn coil in order to reduce the capacitancevalue of a tuning capacitor (not shown) and increase the receive coil'simpedance. By way of example, receive coil 518 may be placed around thesubstantial circumference of device 550 in order to maximize the coildiameter and reduce the number of loop turns (i.e., windings) of thereceive coil 518 and the inter-winding capacitance.

Receive circuitry 510 may provide an impedance match to the receive coil518. Receive circuitry 510 includes power conversion circuitry 506 forconverting a received RF energy source into charging power for use bythe device 550. Power conversion circuitry 506 includes an RF-to-DCconverter 520 and may also in include a DC-to-DC converter 522. RF-to-DCconverter 520 rectifies the RF energy signal received at receive coil518 into a non-alternating power with an output voltage represented byV_(rect). The DC-to-DC converter 522 (or other power regulator) convertsthe rectified RF energy signal into an energy potential (e.g., voltage)that is compatible with device 550 with an output voltage and outputcurrent represented by V_(out) and I_(out). Various RF-to-DC convertersare contemplated, including partial and full rectifiers, regulators,bridges, doublers, as well as linear and switching converters.

Receive circuitry 510 may further include switching circuitry 512 forconnecting receive coil 518 to the power conversion circuitry 506 oralternatively for disconnecting the power conversion circuitry 506.Disconnecting receive coil 518 from power conversion circuitry 506 notonly suspends charging of device 550, but also changes the “load” as“seen” by the transmitter 404 (FIG. 2).

As disclosed above, transmitter 404 includes load sensing circuit 416that may detect fluctuations in the bias current provided to transmitterdriver circuit 424. Accordingly, transmitter 404 has a mechanism fordetermining when receivers are present in the transmitter's near-field.

When multiple receivers 508 are present in a transmitter's near-field,it may be desirable to time-multiplex the loading and unloading of oneor more receivers to enable other receivers to more efficiently coupleto the transmitter. A receiver 508 may also be cloaked in order toeliminate coupling to other nearby receivers or to reduce loading onnearby transmitters. This “unloading” of a receiver is also known hereinas a “cloaking.” Furthermore, this switching between unloading andloading controlled by receiver 508 and detected by transmitter 404 mayprovide a communication mechanism from receiver 508 to transmitter 404as is explained more fully below. Additionally, a protocol may beassociated with the switching that enables the sending of a message fromreceiver 508 to transmitter 404. By way of example, a switching speedmay be on the order of 100 μsec.

In an exemplary embodiment, communication between the transmitter 404and the receiver 508 refers to a device sensing and charging controlmechanism, rather than conventional two-way communication (i.e., in bandsignaling using the coupling field). In other words, the transmitter 404may use on/off keying of the transmitted signal to adjust whether energyis available in the near-field. The receiver may interpret these changesin energy as a message from the transmitter 404. From the receiver side,the receiver 508 may use tuning and de-tuning of the receive coil 518 toadjust how much power is being accepted from the field. In some cases,the tuning and de-tuning may be accomplished via the switching circuitry512. The transmitter 404 may detect this difference in power used fromthe field and interpret these changes as a message from the receiver508. It is noted that other forms of modulation of the transmit powerand the load behavior may be utilized.

Receive circuitry 510 may further include signaling detector and beaconcircuitry 514 used to identify received energy fluctuations, that maycorrespond to informational signaling from the transmitter to thereceiver. Furthermore, signaling and beacon circuitry 514 may also beused to detect the transmission of a reduced RF signal energy (i.e., abeacon signal) and to rectify the reduced RF signal energy into anominal power for awakening either un-powered or power-depleted circuitswithin receive circuitry 510 in order to configure receive circuitry 510for wireless charging.

Receive circuitry 510 further includes processor 516 for coordinatingthe processes of receiver 508 described herein including the control ofswitching circuitry 512 described herein. Cloaking of receiver 508 mayalso occur upon the occurrence of other events including detection of anexternal wired charging source (e.g., wall/USB power) providing chargingpower to device 550. Processor 516, in addition to controlling thecloaking of the receiver, may also monitor beacon circuitry 514 todetermine a beacon state and extract messages sent from the transmitter404. Processor 516 may also adjust the DC-to-DC converter 522 forimproved performance.

FIG. 6 is a schematic diagram of a portion of transmit circuitry 600that may be used in the transmit circuitry 406 of FIG. 4. The transmitcircuitry 600 may include a driver circuit 624 as described above inFIG. 4. As described above, the driver circuit 624 may be a switchingamplifier that may be configured to receive a square wave and output asine wave to be provided to the transmit circuit 650. In some cases thedriver circuit 624 may be referred to as an amplifier circuit. Thedriver circuit 624 is shown as a class E amplifier, however, anysuitable driver circuit 624 may be used in accordance with embodimentsof the invention. 7 The driver circuit 624 may also be provided with adrive voltage V_(D) that is configured to control the maximum power thatmay be delivered through a transmit circuit 650. The drive voltage V_(D)may be provided to a first terminal of an inductor 606. A secondterminal of the inductor 606 is connected to a first terminal of each ofthe switch 604, a capacitor 610 connected across the switch 604, and aninductor 608. A second terminal of the inductor 608 provides an outputto a filter circuit 626, which may be included in the transmit circuitry600 to eliminate or reduce harmonics. The filter circuit 626 may be athree pole (capacitor 634, inductor 632, and capacitor 636) low passfilter circuit 626.

The signal output by the filter circuit 626 may be provided to atransmit circuit 650 comprising a coil 614. The transmit circuit 650 mayinclude a series resonant circuit having a capacitance 620 andinductance (e.g., that may be due to the inductance or capacitance ofthe coil or to an additional capacitor component) that may resonate at afrequency of the filtered signal provided by the driver circuit 624. Theload of the transmit circuit 650 may be represented by the variableresistor 622. The load may be a function of a wireless power receiver508 that is positioned to receive power from the transmit circuit 650.

FIG. 7 is an example wireless communication system 700 in which aspectsof the present disclosure may be employed. The wireless communicationsystem 700 may include a charging pad 701 and a device 702 that may bewirelessly charged.

The charging pad 701 may be plugged into utility power and configured tocouple power wirelessly to the device 702 to be charged. The chargingpad 700 may be connected to the mains utility power and configured toconvert the mains 50/60 Hertz current to a higher frequency ranging fromhundreds of Hertz into the Megahertz. In other aspects, the charging pad701 may convert power to a frequency below hundreds of Hertz or to afrequency above one Megahertz. In some aspects, the power output of thecharging pad 701 may range from a few Watts to approximately 100 Watts.In other aspects, the power output may range below a few Watts or aboveapproximately 100 Watts.

Although the charging pad 701 and the device 702 may be depicted in thisconfiguration, numerous other configurations with different shapes,sizes, and orientations are envisioned and within the spirit of thisdisclosure. As examples, the charging pad surface may be located on anitem such as a refrigerator or built within part of a surface such as akitchen countertop. In other examples, the charging pad 701 surface maybe orientated horizontally such as depicted or vertically such as alongor within a wall. The device 702 could be a smart phone, tabletcomputer, laptop computer, or television, among other possibilities.

FIG. 8 illustrates a side view of an example coil-to-coil couplingsystem 800. The coil-to-coil coupling system 800 may include a primarycoil 801 and a secondary coil 802. The manner of coupling powerwirelessly may be by magnetic coupling of a high frequency alternatingcurrent.

In some aspects, the primary coil 801 may be contained in the chargingpad and energized by the utility mains via electronics also contained inthe charging pad.

In some aspects, the secondary or pickup coil 802 may be contained inthe device 702 to be wirelessly charged. The magnetic field emanatingfrom the primary coil 801 may induce a high frequency alternatingcurrent in the secondary coil 802, which may be rectified and regulatedto charge the battery in the portable device.

The flux lines 803 of the magnetic field may be concentrated in thecenter of the coils in the area between the coils. The flux lines mayconnect to complete the path from one pole of the magnetic field to theother pole. The return path for the flux may be around the periphery ofthe coils. Even with the primary coil 801 and the secondary coil 802nearby, there may be a large air gap that the flux lines may traverse,so the flux may leak into the volume surrounding the coils.

Coupling between the primary coil 801 and secondary coil 802 may beincreased by making each coil resonate with a capacitor, forming tworesonant tank circuits. The increase may be understood in terms of aquality factor or Q factor, which may be a dimensionless parameter thatdescribes the dampened state of an oscillator or resonator. Increasingthe operating Q factor of resonant circuits may increase the coupling.

FIG. 9 illustrates a side view of another example coil-to-coil couplingsystem 900. The coil-to-coil coupling system 900 may include a primarycoil 901, a secondary coil 902, and a backing 904. The manner ofcoupling power wirelessly may be by magnetic coupling of a highfrequency alternating current. The flux lines 903 of the magnetic fieldare depicted.

The backing 904 may improve the coupling between primary coil 901 andsecondary coil 902. The backing 904 may be composed of material with lowmagnetic permeability, such as ferrite. In FIG. 9, the backing 904 isshown for the primary coil 901. In some aspects, this configuration mayafford a low resistance path for the magnetic flux lines to beconcentrated under the primary coil 901 and may avoid coupling energyinto an object under the charging pad 701. In yet other aspects, asecond backing may be used near or above the secondary coil 902. Inaspects where backing may be placed both above and below the coils 901and 902, the magnetic field may be compressed in the vertical directionand may spill out around the edge of the coils.

FIG. 10 illustrates a side view of an example dual coil coupling system1000. The dual coil coupling system 1000 may include primary coils 1001a and 1001 b, secondary coils 1002 a and 1002 b, and a backing 1004. Themanner of coupling power wirelessly may be by magnetic coupling of ahigh frequency alternating current.

The primary coils 1001 a and 1001 b may be adjacent and coplanar. Theprimary coil 1001 a may be counter-wound or connected in oppositepolarity from primary coil 1001 b such that when the field in the upwarddirection from one coil is the north pole, the field upward from theother is the south pole.

The secondary coils 1002 a and 1002 b may be similarly adjacent andcoplanar. In some aspects, the center-to-center spacing between thesecondary coils 1002 a and 1002 b may be approximately the same asbetween the primary coils 1001 a and 1001 b. In other aspects, theprimary coils 1001 a and 1001 b may be in the charging pad 701, and thesecondary coils 1002 a and 1002 b may be in the device 702.

A backing 1004 may be located below the primary coils 1001 a and 1001 b.A second backing (not shown) may be located above the second coils 1002a and 1002 b. The backing 1004 or second backing may be composed ofmaterial such as ferrite. In some aspects, the combination of primarycoils 1001 a and 1001 b, secondary coils 1002 a and 1002 b, and theferrite backings may provide a low permeability magnetic path for theflux lines 1003 to complete the circuit emanating from one primary coil1001 a, concentrated into the center of the opposing secondary coil 1002a, through the second backing, through the second secondary coil 1002 b,concentrated into the center of the other primary coil 1001 b, andcompleting the circuit through the backing 1004. This magnetic circuitmay provide coupling with separation of the primary coils 1001 a and1001 b to the secondary coils 1002 a and 1002 b while low coupling tonearby circuits or objects.

FIG. 11 is a top view of a schematic of an example wirelessly chargeabledevice, such as the device 702 of FIG. 7. The device 702 may containsecondary coils 1102 a and 1102 b, which may be either counter-wound orconnected in opposite polarity to each other. The secondary coils 1102 aand 1102 b may be connected either in series or parallel. The highfrequency alternating magnetic flux induced by primary coils, such asprimary coils 1001 a and 1001 b, may result in a high frequencyalternating current, which may be summed from secondary coils 1102 a and1102 b, rectified and regulated to power the device 702 and may charge abattery. In some aspects, the coils 1102 a and 1102 b may be coplanar.

FIG. 12 is a top view of a schematic of an example charging pad, such asthe charging pad 701 of FIG. 7. The charging pad 701 may include primarycoils 1201 a and 1201 b. In some aspects, the primary coils 1201 a and1201 b may be either counter-wound or connected in opposite polarity toeach other. The primary coils 1201 a and 1201 b may be connected eitherin series or parallel. The primary coils 1201 a and 1201 b may generatea high frequency alternating magnetic flux and result in a highfrequency alternating current in secondary coils, such as secondarycoils 1102 a and 1102 b. In some aspects, the coils 1201 a and 1201 bmay be coplanar.

FIG. 13 is a top view of a schematic of an example charging system 1300,such as the example wireless communication system 700 of FIG. 7. Thedevice 702 shown in FIG. 11 is depicted laying over the primary coils1201 a and 1201 b of the charging pad 701 of FIG. 12. Although the coilcenter-to-center distance may different between the charging pad primarycoils 1201 a and 1201 b, and the device secondary coils 1102 a and 1102b and the device 702 may be misaligned with the coils of the chargingpad, a magnetic circuit may be maintained.

FIG. 14 is a functional block diagram of example components that may beused in a wireless power system, such as the wireless power system ofFIG. 7. The wireless power system 1401 may include a charging pad 1410and portable device 1430. The charging pad 1410 may be connected toutility power 1440, possibly through a stand line cord that plugs into areceptacle. 50/60 Hertz AC utility current may be converted to pulsatingDC current by rectifier 1411. In some aspects, a power factor correctioncircuit 1412 may be used. The pulsating DC current may be smoothed toconstant DC by a filter 1413. The DC current may be chopped into asquare wave by chopper 1414, or a similar DC to ACconverter/transmitter. The current output from the chopper 1414 may besmoothed into a sine wave by filter 1415. In some aspects, filter 1415may match the impedance of the chopper 1414 to the resonant tank circuitmade up of capacitor 1416 and the primary coils 1417. Energy may becoupled from the charging pad 1410 to the portable device 1430 by analternating magnetic field 1450. The alternating magnetic field 1450 maybe coupled into the secondary coils 1431 and converted to an alternatingcurrent. Capacitor 1432 may resonate with the secondary coils 1431 toimprove coupling. Rectifier 1433 may convert the alternating current topulsating DC where it may be filtered into constant DC by capacitor1434. Switch mode power supply 1435 may regulate the current to make itsuitable to power the portable device 1430. In some aspects, a wirelesscommunications link 1470 may be used to coordinate the charging pad andportable device, such as coordinating a charging process between thecharging pad and portable device or coordinating a login process topermit or deny the portable device access to the charging pad.

FIG. 15 is a schematic of an example multi-coil charging pad 1500 thatmay be used in a wireless power system, such as the wireless powertransfer system of FIG. 7. A number of coils may be used to enableplacement of one or more portable devices on the surface of the pad. Insome aspects, the coils may be placed in a grid form as shown in FIG.15. The row 1502 and column 1501 designators are shown only for thisdiscussion and should do not limit the number or configuration of theplacement of coils. In other aspects, the coils may be placed in othernumbers or configurations, including but not limited to any random,equidistant, concentric circle, or oval placement pattern. In someaspects, the coils may be coplanar and may be configured along a flatsurface. In some aspects, the plane of the coils may be curved.

The coils may be formed as copper laminate on an insulating panel orcircuit board, among other possibilities. In some aspects, thecenter-to-center spacing of the coils in the charging pad may beapproximately equal to the center-to-center spacing of the coils in theportable device.

In some aspects, the charging pad 1500 coil polarity shown in FIG. 15may be the default configuration. In yet other aspects, the default coilpolarity may have some other configuration. In operation, the magneticpolarity may be alternating at a high frequency. The magnetic polarityof the individual coils may change over time and independent from oneanother. The coils may be wound in the same direction or arecounter-wound. The magnetic polarity may be switched by reversing theelectrical connection to a coil.

FIG. 16 is a schematic of an example multi-coil charging pad and devicein a wireless power system. FIG. 16 illustrates portable device of FIG.11 atop the charging pad of FIG. 15 in an orientation across a shortdimension of the charging pad. The charging pad coil B2 provides thenorth magnetic pole, and the charging pad coil B3 provides the southmagnetic pole. Since the coils B2 and B3 may be tightly coupled with thecoils of the portable device, the coils B2 and B3 of the charging padmay provide power. The remaining charging pad coils may not be coupledand may provide minimal power.

FIG. 17 is a schematic of an example multi-coil charging pad and devicein a wireless power system. FIG. 17 illustrates portable device of FIG.11 atop the charging pad of FIG. 15 in an orientation turned at a rightangle to the placement in FIG. 16. The charging pad coil B2 provides thenorth magnetic pole, and the charging pad coil C2 provides the southmagnetic pole. Since the coils B2 and C2 may be tightly coupled with thecoils of the portable device, the coils B2 and C2 of the charging padmay provide power. The remaining charging pad coils may not be coupledand may provide minimal power.

FIG. 18 is a schematic of an example multi-coil charging pad and devicein a wireless power system. FIG. 18 illustrates portable device of FIG.11 atop the charging pad of FIG. 15 turned in a diagonal orientation. Inthis case, an alternating checkerboard pattern of coil polarity mayresult in the coils of the portable device lying over charging pad coilsof the same polarity. In some aspects, the polarity of rows 2 and 4 maybe switched so that each coil in those rows has the opposite polarityfrom the configuration in FIG. 15. In some aspects, the rows 2 and 4 maybe switched with a single switch double pole, double throw type. Inother aspects, the rows may be switched using other methods. Afterswitching, one north and one south pole charging pad coil may be locatedunder the diagonally placed portable device.

FIG. 19 is a schematic diagram of an example switching circuit to changethe polarity of charging pad coils. With the double pole, double throwswitch S in the upper position, the coils may be connected in thedefault configuration, such as the configuration shown in FIGS. 15, 16,and 17. With the double pole, double throw switch S in the lowerposition rows 2 and 4 have the opposite polarity shown in FIG. 18. Theswitch may be a mechanical switch or relay, or the switch may be anymanner of electronic switch, such as a MOSFET. The decision of whetherto position the switch in the upper or lower position may be made byproviding short bursts of power with the switch in each position andselecting the switch position that draws the most power. In someaspects, other position sensing or power sensing schemes may be used. Insome aspects, individual charging pad coils may use individual switchingor sensing circuits.

FIG. 20 is a schematic of an example multi-coil charging pad and devicein a wireless power system. Each coil of the charging pad may beindividually controlled and turned on or off. Charging power may berouted to some charging pad coils. In the case shown in FIG. 20,charging pad coils B2 and C3 may provide better coupling to the portabledevice oriented diagonally on the charging pad. Charging pad coils B2and C3 may be turned on while the remaining coils may be turned off.

FIG. 21 is a schematic diagram of an example switching circuit to changethe polarity of charging pad coils. Each coil 2110 may have anassociated H-bridge switch 2100. In some aspects, the H-bridge switchmay be made up of four power transistors or MOSFETs arranged to connectthe coil to the power rails 2101, 2102. In operation, two of thetransistors may be active at a time. In some aspects, the upper lefttransistor may be turned on to connect the upper lead of the coil to theupper power rail 2101 while the lower right transistor may be turned onto connect the lower lead of the coil to the lower power rail 2102. Theother two transistors may be turned off. In the other aspects, the upperright transistor may be turned on to connect the lower coil lead to theupper power rail 2101 while the lower left transistor may be turned onto connect the upper lead of the coil to the lower power rail 2102,changing the polarity of the coil connections. The other two transistorsmay be turned off.

FIG. 22 is a schematic of an example multi-coil charging pad andmultiple devices in a wireless power system. One device may be coupledto charging pad coils B2 and C3 while a second device may be coupled tocharging pad coils E1 and E3. Coil E1 may be used rather than coil E2.Charging pad coil E1 and the upper coil in the portable device may bemisaligned, the magnetic circuit may still form in the closed loop asdepicted in FIG. 10.

The coil polarity configurations illustrated in FIGS. 15, 16, 17, and 18may not simultaneously satisfy the alignment of both devices shown inFIG. 22. In some aspects, the polarity of rows 2 and 4 may be rapidlyswitched while the portable devices alternately may turn off theircoupling to the charging pad and may turn on when a particular polaritymay be presented.

FIG. 23 is an example wireless power transmitter which includes a powertransfer sensing mechanism that may be used to determine a measure ofcoupling of power between coils or pairs of coils. Although FIG. 23illustrates one transmit coil 2314, a plurality of transmit coils may besimilarly configured and controlled by one or more controllers, such asthe controller 2315. In combination, the plurality of transmit coils andone or more controllers may be configured to create a multi-coilcharging pad, such as the charging pad 1500 illustrated in FIG. 15.Based on the measure of coupling between coils or pairs of coils in themulti-coil charging pad, the one or more controllers may be configuredto select coils or pairs of coils for wireless power transmission, forinstance, by energizing or de-energizing one or more coils as describedin the discussion of FIG. 20. In some aspects, based on the measure ofcoupling between coils or pairs of coils in the multi-coil charging pad,the one or more controllers may be configured to reverse the polarity ofone or more coils of the plurality of coils as described in thediscussion of FIG. 22, for example.

As shown in FIG. 23, three wireless power receivers 2308A, 2308B, and2308C may be configured to be coupled to a wireless field to receivepower. Each of the wireless power receivers 2308A-2308C may include aresonant circuit (e.g., resonant circuits 2309A-2309C) having a wirelesspower receiver coil coupled to a one or more capacitors. The resonantcircuits 2309A-2309C or each wireless power receiver 2308A-2308C arecoupled to a rectification circuit (e.g., rectification circuits2311A-2311C) to output a voltage at a voltage level for powering orcharging a corresponding load (not shown). For example, the firstwireless power receiver 2308A may be configured to output a voltage at avoltage level V_(out1), the second wireless power receiver 2308B may beconfigured to output a voltage at a voltage level V_(out2), and thethird wireless power receiver 2308C may be configured to output avoltage at a voltage level V_(out3). The voltage levels V_(out1),V_(out2), and V_(out3) may be set to meet the load requirements coupledto each of the wireless power receivers 2308A-2308C.

Further, as shown in FIG. 23, a power source 2322 is configured toprovide a voltage signal V_(D) to each of a first and second drivingcircuit 2370 and 2380. For example, each of the first and second drivingcircuits 2370 and 2380 may be configured as class E amplifiers which areconnected to drive a wireless power transmit coil 2314 in a push-pullconfiguration. The first driving circuit 2370 includes a first voltagesource 2372 configured to generate a voltage signal at a voltage levelV₁. The output of the first voltage source 2372 is coupled to a firstswitching circuit 2374. The first switching circuit 2374 is coupled to avoltage signal (V_(D)) terminal input to receive a power signal throughan inductor 2376. The output of the first switching circuit 2374 iscoupled to a wireless power field generating circuit through the firstbypass capacitor 2378. Based on the relative value of voltage signalV_(D) and the voltage level V₁, the first driving circuit 2370 isconfigured to inject current into the wireless power field generatingcircuit.

The second driving circuit 2380 includes similar components andfunctions similar to the first driving circuit 2370. For example, asshown in FIG. 23, the second driving circuit 2380 includes a secondvoltage source 2382 configured to generate a voltage signal at a voltagelevel V₂. The second voltage source 2382 is coupled to second switchingcircuit 2384. The second switching circuit 2384 is coupled to a voltagesignal (V_(D)) terminal input to receive power signal through aninductor 2386. The output of the second switching circuit 2384 iscoupled to wireless power field generated circuit through the secondbypass capacitor 2388. Based on the relative value of voltage signalV_(D) and the voltage level V₂, the second driving circuit 2380 isconfigured to inject current into the wireless power field generatingcircuit.

A current from the first and second driving circuit and 2370 and 2380 isreceived by a wireless power transmit coil 2314 to generate the wirelesspower transfer field. The wireless power transmit coil 2314 is coupledto each of the first and second driving circuit 2370 and 2380 throughfirst and second inductive components 2392 and 2393, and first throughfourth capacitive components 2394-2397. The inductive components 2392,2393, and capacitive components 2394-2397 may be coupled to the wirelesspower transmit coil 2314 to form a resonant circuit. As shown in FIG.23, the wireless power transmit coil 2314 is also coupled to coilimpedance adjustment circuit 2390, a current sensor 2360, and a voltagesensor 2350. While shown to include each of a current sensor 2360,voltage sensor 2350, and coil impedance adjustment circuit 2390, thetransmit circuitry may also include any combination of these componentsincluding, for example, only one of these components. Further, variouscomponents illustrated and/or described in FIG. 23 and additionalcomponents may be included or excluded based on the functionality of awireless power transmitter.

As shown in FIG. 23, the coil impedance adjustment circuit 2390 may beconfigured to adjust the impedance of the wireless power transmit coilbased on a signal received from controller 2315 in order to control theamount of current flowing through the wireless power transmit coil 2314.The current sensor 2316 may be coupled to the wireless power transmitcoil 2314 in series, and may be configured to detect the level ofcurrent passing through the wireless power transmit coil 2314 andcommunicate the sensed level of current to the controller 2315. Thevoltage sensor 2350 may be configured to detect a voltage level at theinput of wireless power transmit coil 2314 and communicate the detectedvoltage level to the controller 2315. Additionally, or alternatively,the voltage sensor 2350 may be configured to detect a voltage level(ReF1, ReF2) across an impedance (e.g., capacitive component 2397 asshown in FIG. 23) and communicate the detected voltage difference to thecontroller 2315. The controller 2315 may be configured to determine acurrent through the wireless power transmit coil 2314 based on thedetected voltage levels (e.g., ReF1 and ReF2). Further, the voltagesensor 2350 may be configured to detect a voltage level across thetransmit coil 2314 (e.g., a voltage equal to ReF2-ReF3) and transmit thedetected voltage level to the controller 2315. Other voltagemeasurements and current measurements may also be performed and providedto the controller 2315, and the illustrated examples of FIG. 23 areprovided only as example measurement positions.

The controller 2315 may be configured to adjust a parameter of thetransmit circuitry, for example by adjustment of one or more of aneffective impedance of the transmit coil 2314 (e.g. through control ofthe coil impedance adjustment circuit 2390) and the level of the drivevoltage V_(D) to maintain a constant current through the coil 2314 or aconstant voltage at the transmit coil 2314. Further, the controller 2315may be configured to determine a measure of coupling of power betweencoils or pairs of coils based on the product of the detected voltagelevel across the transmit coil 2314 and determined current through thetransmit coil 2314, for example. In some aspects, as another example,the controller 2315 may be configured to determine a measure of couplingof power between coils or pairs based on fluctuations in the detectedcurrent through the transmit coil 2314. Based in part on the measure ofcoupling of power between coils or pairs of coils, the controller 2315may selectively energize or de-energize the transmit coil 2314 (e.g., bysufficiently decreasing the current through the transmit coil 2314) orreverse polarity of the magnetic field of the transmit coil 2314.

According to some embodiments, the controller 2315 may be configured togenerate an internal or local feedback signal to adjust one of thecurrent through the wireless power transmit coil 2314 and the voltage atthe input of the wireless power transmit coil 2314. For example, thecontroller 2315 may also be configured to provide a feedback signal 2323(e.g., a local or internal feedback signal) for controlling the voltagelevel of the power signal generated by the power source 2322.Additionally, or alternatively, the controller 2315 may be configured togenerate a feedback signal (e.g., a local or internal feedback signal)to adjust the effective impedance of the wireless power transmit coil2314 by adjusting the impedance of the coil impedance adjustment circuit2390. The controller 2315 may be configured to control a set of switchesof the coil impedance adjustment circuit 2390 which are configured toconnect one or more reactive and resistive elements in parallel orseries with the wireless power transmit coil 2314. If the currentmeasurement is lower than a predetermined threshold the switches will beconfigured to reduce the impedance of the primary winding. In this way,the controller 2315 may be configured to maintain constant level ofcurrent through the wireless power transmit coil 2314 in the presence ofa plurality of wireless power receivers 2308A-2308C and differentloading conditions as discussed above. Alternatively, the controller2315 may be configured to maintain constant voltage level at the inputof the wireless power transmit coil 2314 in the presence of a pluralityof wireless power receivers 2308A-2308C and different loading conditionsas discussed above.

Further, a wireless power transmitter may include a communication module2317 coupled to the controller 2315. The communication module 2317 maybe configured to receiver communication signals from one or more of thewireless power receivers 2308A-2308C. Based on the communicationsignals, the controller 2315 may also determine an adjustment of one ofthe currents through wireless power transmit coil 2314 and a voltage atthe input of the wireless power transmit coil. For example, the wirelesspower receivers 2308A-2308C may provide feedback to the controller 2315based on the power received by each of the wireless power receivers2308A-2308C and the requirements of each of the wireless power receivers2308A-2308C. In some embodiments, the controller 2315 may use thecommunication signals received from the wireless power receivers2308A-2308C to adjust a set-point for one of the current and voltage ofthe wireless power transmit coil 2314. The controller 2315 may also usethe local or internal feedback (e.g., based on signals received from thevoltage sensor 2350 and current sensor 2360) to adjust one of thevoltage and current of the wireless power transmit coil 2314. Forexample, the controller 2315 may be configured to perform a coarseadjustment based on signals received from the wireless power receivers2308A-2308C, and a fine adjustment based on signals received from thevoltage sensor 2350 or the current sensor 2360.

FIG. 24 is a flowchart of an example alignment discovery logic 2400 fora charging pad. Using the alignment discovery logic 2400, the chargingpad may determine which charging pad coils to energize to couple to oneor more portable devices placed on the charging pad.

At block 2405, the charging pad may use low power pulses to each coil orconfiguration of coils to determine whether a coil or configuration maybe coupling with a device. At block 2410, the device may sense the powerpulses and respond with the strength of coupling. At blocks, 2415 and2420, if the charging pad may determine that a particular coil orconfiguration may not be coupling, the charging pad may turn off thecoil or configuration for a duration of time to save power, for example.In some aspects, the duration of time may be predetermined. After theduration of time passes, the charging pad may repeat the low powerpulses to each coil or coil configuration.

At blocks 2415 and 2425, if the charging pad determines that aparticular coil or configuration of coils may couple power to thedevice, the charging pad may select candidate coils for wireless powertransmission. At block 2430, the candidate coils may be pulsed in pairs.At block 2435, the device may sense the power pulses and respond withthe strength of coupling. At block 2440, the charging pad may determineparticular candidate pairs of coils that may result in a greatertransfer of power than other candidate pairs of coils and select thoseparticular candidate pairs for wireless transfer of power. At blocks2445 and 2450, power may be turned on to the selected candidate pairs,and the device may switch to a charging state.

In some aspects, the portable device may connect a nominal load to eachportable device coil when in a non-charging state (e.g., when not on acharging pad). The portable device may be placed on a charging pad whilein a non-charging state, and the nominal load may accept some power fromthe charging pad.

In some aspects, the portable device may communicate power coupled byeach coil and reactance modulate the low power pulses from the chargingpad. The nominal load may be connected and disconnected in a pattern tosignal the coupling strength and provide a measure of coupling betweencoils. In some aspects, the coupling strength may be communicated over acommunication link 1470 shown in FIG. 14. In yet other aspects, thecharging pad may measure the voltage or current in the charging padcoils and sense which coils may couple power to the portable device. Thecharging pad may sense a load and select a combination of coils or coilconfiguration and may turn on charging power. The portable device mayuse power coupled from the charging pad to charge a battery or power thedevice. In some aspects, the portable device may switch from chargingthe battery to powering the device, or vice versa. In some aspects, thealignment discovery logic 2400 may be used in a device 702 to controlthe receipt of power by the individual coils of the device.

FIG. 25 is a top view of a schematic of an example wirelessly chargeabledevice 2500, such as device 702 of FIG. 7. The number of coils in theportable device may be increased to four (e.g., coils 2501 a, 2501 b,2501 c and 2501 d). In other aspects, the number of coils may beincreased to larger numbers. Increasing the number of coils may improvedelivery of power to larger or power hungry devices and may increase thechances of efficient coupling of coils.

FIG. 26 is a schematic of an example multi-coil charging pad and devicein a wireless power system. FIG. 26 illustrates portable device of FIG.25 atop a charging pad where the portable device may be centered at theintersection between four charging pad coils. In this configuration, thecharging pad coils B2, B3, and B4 may provide the north polarity, columnC may be turned off because of the overlap between opposite polaritycoils in the portable device, and charging pad coils D2, D3 and D4 mayprovide the south polarity. In other aspects, different charging padcoils may be turned on or off.

FIG. 27 is a schematic of an example multi-coil charging pad and devicein a wireless power system. FIG. 27 illustrates portable device of FIG.25 atop a charging pad where the portable device may be placeddiagonally on the charging pad. In this configuration, the charging padcoil C3 may be turned off while charging pad coils B3 and C2 may providethe north polarity and charging pad coils C4 and D3 may provide thesouth polarity. In other aspects, different charging pad coils may beturned on or off.

FIG. 28 is flowchart of an example method 2800 of transmitting wirelesspower in accordance with aspects. The method 2800 may be used totransmit power wirelessly from a charging pad as illustrated in FIG. 7,for example. Although the method 2800 is described below with respect tothe elements of the Figures contained in this disclosure, those havingordinary skill in the art will appreciate that other components may beused to implement one or more of the steps described herein. In anembodiment, the method 2800 may be performed by the controller 415 andother components of the transmitter 404, for example. Although themethod of flowchart 2800 is described herein with reference to aparticular order, in various embodiments, blocks herein may be performedin a different order, or omitted, and additional blocks may be added.

At block 2805, a plurality of coplanar coils may be energized so thateach of the plurality of coplanar coils produces a magnetic field. Forexample, the charging pad 1410 may energize the primary coils 1417.

At block 2810, the polarity of the magnetic field of at least one of aplurality of coplanar coils may be reversed based on a measure ofcoupling between coils. The circuit illustrated in FIG. 14, 19, or 21may be utilized in conjunction with the controller 415 of thetransmitter 404 to perform these actions, for example.

At block 2815, at least two of the plurality of coplanar coils may beselected for wireless power transmission. The circuit illustrated inFIG. 14, 19, 21, or 23 may be utilized in conjunction with thecontroller 415 to perform these actions, for example.

FIG. 29 is a functional block diagram of a wireless power apparatus2900. The wireless power apparatus 2900 includes an energizing module2905, a polarity reversing module 2910, and a selecting module 2915. Theenergizing module 2905 may include a means for energizing a plurality ofcoplanar coils so that each of the plurality of coplanar coils producesa magnetic field. In some aspects, the energizing module 2905 may beconfigured to perform one or more of the functions discussed above withrespect to the block 2805. The polarity reversing module 2910 mayinclude a means for reversing polarity of the magnetic field of at leastone of the plurality of coplanar coils based on a measure of couplingbetween coils. In some aspects, the polarity reversing module 2910 maybe configured to perform one or more of the functions discussed abovewith respect to the block 2810. The selecting module 2915 may includemeans for selecting at least two of the plurality of coplanar coils forwireless power transmission based on the measure of coupling betweencoils. In some aspects, the selecting module 2915 may be configured toperform one or more of the functions discussed above with respect to theblock 2815.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.Means for energizing may be provided by the charging pad 1410 and theprimary coils 1417. Means for reversing the polarity may be providedusing the circuit illustrated in FIGS. 19 and 21. Means for selectingmay be provided by the controller 415. Means for reversing based on areceived signal strength may be provided using the circuit illustratedin FIGS. 19 and 21 and by the controller 415 and wireless communicationslink 1470. Means for energizing or de-energizing may be provided by thecontroller 415.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that may bereferenced throughout the above description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. The described functionalitymay be implemented in varying ways for each particular application, butsuch implementation decisions should not be interpreted as causing adeparture from the scope of the embodiments of the invention.

The various illustrative blocks, modules, and circuits described inconnection with the embodiments disclosed herein may be implemented orperformed with a general purpose processor, a Digital Signal Processor(DSP), an Application Specific Integrated Circuit (ASIC), a FieldProgrammable Gate Array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm and functions described in connectionwith the embodiments disclosed herein may be embodied directly inhardware, in a software module executed by a processor, or in acombination of the two. If implemented in software, the functions may bestored on or transmitted over as one or more instructions or code on atangible, non-transitory computer-readable medium. A software module mayreside in Random Access Memory (RAM), flash memory, Read Only Memory(ROM), Electrically Programmable ROM (EPROM), Electrically ErasableProgrammable ROM (EEPROM), registers, hard disk, a removable disk, a CDROM, or any other form of storage medium known in the art. A storagemedium is coupled to the processor such that the processor can readinformation from, and write information to, the storage medium. In thealternative, the storage medium may be integral to the processor. Diskand disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer readable media. The processor andthe storage medium may reside in an ASIC. The ASIC may reside in a userterminal. In the alternative, the processor and the storage medium mayreside as discrete components in a user terminal.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment of the invention.Thus, the invention may be embodied or carried out in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other advantages as may be taughtor suggested herein.

Various modifications of the above described embodiments will be readilyapparent, and the generic principles defined herein may be applied toother embodiments without departing from the spirit or scope of theinvention. Thus, the present invention is not intended to be limited tothe embodiments shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

What is claimed is:
 1. An apparatus for wireless power transmission,comprising: a plurality of coplanar coils, each of the plurality ofcoplanar coils configured to be individually energized and produce amagnetic field; and a controller configured to reverse polarity of themagnetic field of at least one of the plurality of coplanar coils basedon a measure of coupling between individual coils of the plurality ofcoils and at least one receiver coil and to select at least two of theplurality of coplanar coils for wireless power transmission based on themeasure of coupling between the individual coils of the plurality ofcoils and the at least one receiver coil.
 2. The apparatus of claim 1,wherein the measure of coupling between the individual coils of theplurality of coils and the at least one receiver coil comprises ameasure of coupling of power between the individual coils of theplurality of coils and the at least one receiver coil.
 3. The apparatusof claim 1, wherein the measure of coupling between coils comprises ameasure of coupling of power between at least two of the plurality ofcoplanar coils and the at least one receiver coil, wherein the at leasttwo of the plurality of coplanar coils and the at least one receivercoil form a closed magnetic loop.
 4. The apparatus of claim 1, whereinthe controller is further configured to energize or de-energize at leastone of the plurality of coplanar coils based on a measure of couplingbetween the individual coils of the plurality of coils and the at leastone receiver coil.
 5. The apparatus of claim 1, wherein each of theplurality of coplanar coils is configured to have an opposite magneticpolarity to an adjacent coil.
 6. The apparatus of claim 1, wherein theplurality of coplanar coils are configured in rows and columns.
 7. Theapparatus of claim 6, wherein the controller is further configured tocause the polarity of a row of coils or a column of coils to be the samepolarity.
 8. The apparatus of claim 6, wherein the controller is furtherconfigured to cause the polarity of each of the plurality of coplanarcoils to have an opposite magnetic polarity to a directly adjacent coil.9. A method for wireless power transmission, comprising: energizing aplurality of coplanar coils so that each of the plurality of coplanarcoils produces a magnetic field; reversing polarity of the magneticfield of at least one of the plurality of coplanar coils based on ameasure of coupling between individual coils of the plurality of coilsand at least one receiver coil; and selecting at least two of theplurality of coplanar coils for wireless power transmission based on themeasure of coupling between the individual coils of the plurality ofcoils and at least one receiver coil.
 10. The method of claim 9, whereinthe measure of coupling between the individual coils of the plurality ofcoils and the at least one receiver coil comprises a measure of couplingof power between coils.
 11. The method of claim 9, wherein the measureof coupling between the individual coils of the plurality of coils andthe at least one receiver coil comprises a measure of coupling of powerbetween at least two of the plurality of coplanar coils and the at leastone receiver coil, wherein the at least two of the plurality of coplanarcoils and the at least one receiver coil form a closed magnetic loop.12. The method of claim 9, further comprising energizing orde-energizing at least one of the plurality of coplanar coils based on ameasure of coupling between the individual coils of the plurality ofcoils and the at least one receiver coil.
 13. The method of claim 9,wherein each of the plurality of coplanar coils is configured to have anopposite magnetic polarity to an adjacent coil.
 14. The method of claim9, wherein the plurality of coplanar coils are configured in rows andcolumns.
 15. The method of claim 14, further comprising causing thepolarity of a row of coils or a column of coils to be the same polarity.16. The method of claim 14, further comprising causing the polarity ofeach of the plurality of coplanar coils to have an opposite magneticpolarity to a directly adjacent coil.
 17. An apparatus for wirelesspower transmission, comprising: means for energizing a plurality ofcoplanar coils so that each of the plurality of coplanar coils producesa magnetic field; means for reversing polarity of the magnetic field ofat least one of the plurality of coplanar coils based on a measure ofcoupling between coils; and means for selecting at least two of theplurality of coplanar coils for wireless power transmission based on themeasure of coupling between individual coils of the plurality of coilsand at least one receiver coil.
 18. The apparatus of claim 17, whereinthe measure of coupling between the individual coils of the plurality ofcoils and the at least one receiver coil comprises a measure of couplingof power between the individual coils of the plurality of coils and theat least one receiver coil.
 19. The apparatus of claim 17, wherein themeasure of coupling between the individual coils of the plurality ofcoils and the at least one receiver coil comprises a measure of couplingof power between at least two of the plurality of coplanar coils and theat least one receiver coil, wherein the at least two of the plurality ofcoplanar coils and the at least one receiver coil form a closed magneticloop.
 20. The apparatus of claim 17, further comprising means forenergizing or de-energizing at least one of the plurality of coplanarcoils based on a measure of coupling between the individual coils of theplurality of coils and the at least one receiver coil.
 21. The apparatusof claim 17, wherein each of the plurality of coplanar coils isconfigured to have an opposite magnetic polarity to an adjacent coil.22. The apparatus of claim 17, wherein the plurality of coplanar coilsare configured in rows and columns.
 23. The apparatus of claim 22,further comprising means for causing the polarity of a row of coils or acolumn of coils to be the same polarity.
 24. The apparatus of claim 22,further comprising means for causing the polarity of each of theplurality of coplanar coils to have an opposite magnetic polarity to adirectly adjacent coil.
 25. A non-transitory computer storage thatstores executable program instructions that direct an apparatus forwireless power transmission to perform a process that comprises:energizing a plurality of coplanar coils so that each of the pluralityof coplanar coils produces a magnetic field; reversing polarity of themagnetic field of at least one of the plurality of coplanar coils basedon a measure of coupling between individual coils of the plurality ofcoils and at least one receiver coil; and selecting at least two of theplurality of coplanar coils for wireless power transmission based on themeasure of coupling between coils.
 26. The non-transitory computerstorage of claim 25, wherein the measure of coupling between theindividual coils of the plurality of coils and the at least one receivercoil comprises a measure of coupling of power between the individualcoils of the plurality of coils and the at least one receiver coil. 27.The non-transitory computer storage of claim 25, wherein the measure ofcoupling between the individual coils of the plurality of coils and theat least one receiver coil comprises a measure of coupling of powerbetween at least two of the plurality of coplanar coils and the at leastone receiver coil, wherein the at least two of the plurality of coplanarcoils and the at least one receiver coil form a closed magnetic loop.28. The non-transitory computer storage of claim 25, wherein the processfurther comprises energizing or de-energizing at least one of theplurality of coplanar coils based on a measure of coupling between theindividual coils of the plurality of coils and the at least one receivercoil.
 29. The non-transitory computer storage of claim 25, wherein eachof the plurality of coplanar coils is configured to have an oppositemagnetic polarity to an adjacent coil.
 30. The non-transitory computerstorage of claim 25, wherein the plurality of coplanar coils areconfigured in rows and columns.
 31. The non-transitory computer storageof claim 30, wherein the process further comprises causing the polarityof a row of coils or a column of coils to be the same polarity.
 32. Thenon-transitory computer storage of claim 30, wherein the process furthercomprises causing the polarity of each of the plurality of coplanarcoils to have an opposite magnetic polarity to a directly adjacent coil.